Surface induced ring-opening polymerization and medical devices formed therefrom

ABSTRACT

The present disclosure relates to coated biodegradable materials having a reduced amount of residual catalysts and methods thereof.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is Divisional Application claiming the benefitof and priority to U.S. patent application Ser. No. 13/208,525, filedAug. 12, 2011, which claims the benefit of and priority to U.S.Provisional Application Ser. No. 61/407,610, filed on Oct. 28, 2010, theentire disclosures of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to methods of inducing ring-openingpolymerization on a surface of biodegradable polymeric materials and themedical devices formed therefrom.

2. Background of Related Art

Polyesters represent a commercially important class of polymers. Oneroute to forming polyesters is via ring-opening polymerization of cyclicesters. For example, ε-caprolactone can by polymerized topolycaprolactone, which is widely used as a biocompatible material forthe fabrication of implantable devices. Known ring-openingpolymerization methods may require the addition of a catalyst to drivethe reaction. Such methods often produce polymers which include residualamounts of the catalysts. That is to say, not all of the catalystprovided to drive the polymerization reaction may be utilized therebybeing left within the polymeric material. The residual or excesscatalyst is an impurity which may make decrease the strength of thepolymeric material. In addition, upon degradation, the release of theresidual catalyst from the polymeric material may be toxic to theenvironment and/or the patient in which the polymeric material isimplanted. Therefore, a need exists for improving polymerizationprocesses which produce biodegradable polymeric materials includingreduced amounts of impurities and/or reduced amount of residualcatalysts.

SUMMARY

Accordingly, methods are described herein for reducing the amount of aresidual catalyst from a biodegradable polymeric material. The methodsinclude: providing a container which includes at least one monomercapable of polymerizing via cationic ring-opening polymerization and abiodegradable polymeric material containing an amount of a residualcatalyst; and, heating the container above the glass transitiontemperature of the biodegradable polymeric material and below thecrystallization temperature of the biodegradable polymeric material fora period of time sufficient to reduce the amount of residual catalyst inthe biodegradable polymeric material.

In some methods, the container may include a heating means. In otherembodiments, the container may be positioned within a separate heatingmeans, such as an oven.

In certain embodiments, methods of grafting a biodegradable coating ontoa surface of a biodegradable polymeric material are described. Themethods include: providing a container which includes at least onemonomer capable of polymerizing via cationic ring-openingpolymerization, positioning a biodegradable polymeric materialcontaining an amount of a residual catalyst in the container, andplacing the container with the biodegradable polymeric material in anoven for a period of time, wherein the oven is heated above the glasstransition temperature and below the crystallization temperature of thebiodegradable polymeric material. The container may be heated for aperiod of time sufficient to reduce the amount of residual catalyst inthe biodegradable polymeric material and/or provide the substrate with abiodegradable coating grafted to a surface of the substrate.

In still other embodiments, methods of inducing ring-openingpolymerization of an aliphatic cyclic ester monomer on a surface of amedical device are also described. Such methods include: providing aclosed container which includes an aliphatic cyclic ester monomer and amedical device made from a cyclic aliphatic ester; and, heating theclosed container to at least a glass transition temperature of thecyclic aliphatic ester of the medical device and below thecrystallization temperature of the cyclic aliphatic ester of the medicaldevice to induce ring-opening polymerization of the aliphatic cyclicester monomer along the surface of the medical device. The medicaldevice may include a first amount of residual catalyst prior to beingheated and a second different amount of residual catalyst after beingheated, wherein the first amount is higher than the second amount ofresidual catalyst.

The coated biodegradable polymeric materials containing a reduced amountof residual catalyst are also described herein. In embodiments, thebiodegradable polymeric materials may be in a pellet format. In someembodiments, the biodegradable polymeric materials may be in the form ofan implantable medical device. The biodegradable polymeric materialsinclude a substrate containing a reduced amount of residual catalyst,and a biodegradable coating positioned on at least a portion of thesubstrate, wherein the coating is grafted via interpenetratingmechanisms through a surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing, which is incorporated in and constitutes apart of this specification, illustrates embodiments of the disclosureand, together with a general description of the disclosure given above,and the detailed description of the embodiments given below, serves toexplain the principles of the disclosure.

FIG. 1A shows a biodegradable polymeric material prior to the methodsdescribed herein.

FIG. 1B shows a coated biodegradable polymeric material in accordancewith one embodiment of the present disclosure.

FIG. 2A shows a biodegradable polymeric material prior to the methodsdescribed herein.

FIG. 2B shows a coated biodegradable polymeric material in accordancewith another embodiment of the present disclosure.

DETAILED DESCRIPTION

The present disclosure describes methods of inducing ring-openingpolymerization on the surface of a biodegradable polymeric material.Such methods provide a coating on the biodegradable polymeric materials.In addition, such methods reduce the amount of residual catalysts in thebiodegradable polymeric material thereby purifying and strengthening thematerial.

Unlike other known coating processes, the methods described herein donot require the use of a solvent to form the coating and as a result thebiodegradable polymeric materials may include a coating made from a“friendlier” polymer, i.e., less toxic to the patient and/orenvironment, without compromising the mechanical strength of thebiodegradable polymeric material. Such methods provide coatedbiodegradable polymeric materials wherein the coating is physicallygrafted (i.e., interpenetrating mechanisms) through a surface to a depthin the biodegradable polymeric material. Such coatings may improve themechanical strength of the biodegradable polymeric material. Thecoatings may be continuous or discontinuous along the polymericmaterial.

Initially, at least one monomer capable of polymerizing via ring-openingpolymerization and/or at least one biodegradable polymeric materialincluding a first amount of residual catalyst may be positioned within acontainer, i.e., reaction vessel. It is envisioned that the monomer andthe biodegradable polymeric material may be positioned within thecontainer in any order. The container may then be sealed and thecontents positioned within the container may be heated above the glasstransition temperature and below the crystallization temperature of thebiodegradable polymeric material.

The polymeric materials described herein may include amorphous andcrystalline portions. Heating a polymeric material above its respectiveglass transition temperature will reversibly change the amorphousportions of the polymeric material from a hard, glassy, or brittlecondition to a flexible or elastomeric condition. Conversely, coolingthe polymeric material below its respective glass transition temperaturewill reversibly change the amorphous portions of the polymeric materialfrom a flexible or elastomeric condition to a hard, glassy, or brittlecondition. The glass transition temperature for each polymeric materialmay be different.

The crystallization temperature represents the temperature at which thecrystalline portions of a polymeric material begin to become organizedcrystals. The crystallization temperature is often higher than the glasstransition temperature of a polymeric material and lower than themelting temperature of the polymeric material. Unlike the meltingtemperature, as the polymeric material approaches the crystallizationtemperature, the crystalline portions of the polymeric materials willbegin to organize as crystals thereby producing an exothermic reactionor providing heat to the area surrounding the polymeric material. It isenvisioned that this additional heat or energy may further drive thering-opening polymerization processes described herein.

Heating of the biodegradable polymeric material above the glasstransition temperature and below the crystallization temperature of thepolymeric material allows the amorphous portions of the biodegradablepolymeric material to soften, creating less dense regions, such as poresin the surface of the biodegradable polymeric material. In embodiments,the softening and/or pores of the biodegradable polymeric material Myallow the residual catalyst to be released to a surface of thebiodegradable material and interact with the monomer positioned in thecontainer. In certain embodiments, the softening and/or pores of thebiodegradable polymeric material allows the monomer to enter the surfaceof the biodegradable material and interact with the residual catalystpositioned in the polymer. It is envisioned that the residual catalystwill polymerize the monomer via ring-opening polymerization along thesurface of the material thereby forming a coating layer on the material.In embodiments, the monomer may interact with the residual catalyst andpenetrate a certain depth below the surface of the material creating agrafted coating via interpenetrating mechanisms through a surface of thepolymeric material.

In some embodiments, an aliphatic cyclic ester monomer, such asε-caprolactone, may be placed in the container with an implantablemedical device made from polylactide which includes a first amount of aresidual catalyst such as stannous octoate. In embodiments, the monomermay not include a solvent. The temperature inside the container may beheated to a temperature slightly above the glass transition temperatureand below the crystallization temperature of the polylactide suturematerial, i.e., to between about 70° C. and about 80° C., to soften theamorphous phase of the polylactide suture material. Softening of theamorphous phase of the suture material may subsequently lead to enhanceddiffusion of the residual catalyst out of the suture material, as wellas enhance diffusion of the monomer into the surface layer of the suturematerial. The monomer and the residual catalyst may interact to form apoly(caprolactone) coating on the surface of polylactide suture materialand the polylactide suture material will include a second amount ofresidual catalyst which is less than the first amount of residualcatalyst. More specifically, the monomer undergoes ring-openingpolymerization on the surface of the medical device, the reaction drivenby the stannous octoate.

The container or reaction vessel includes a sealable door through whichone or more monomers and/or biodegradable polymeric materials may passto be placed or removed from the reaction vessel. While thebiodegradable polymeric materials may be placed into the reaction vesselin any manner or position, the greater the surface area of thebiodegradable polymeric materials that is accessible to the monomer, themore likely the monomer is to come into contact with residual catalystand form a grafted coating on the biodegradable polymeric materials. Insome embodiments, a rack adapted to hold the one or more biodegradablepolymeric materials may be placed within the reaction vessel. Forexample, in some embodiments, biodegradable polymeric materials such assutures may be wound on a spool or a rack and placed within the reactionvessel.

The interior of reaction vessel can be advantageously made from or linedwith a material that is non-reactive with the biodegradable polymericmaterials and/or the monomer. Such non-reactive materials includestainless steel, glass and the like. It is also contemplated that theinterior of the reaction vessel can be passivated to make the interiorsurface less reactive. Passivation techniques are within the purview ofthose skilled in the art.

In embodiments, the reaction vessel may include any number of additionalsupport means suitable for performing the methods described herein. Somenon-limiting examples include a mixer, pressurizer, sprayer, heater,circulator, timer, computer, filter, waste lines, overflow tanks,sensors, and the like. In some embodiments, the reaction vessel iscapable of heating the contents within the vessel. In embodiments, thereaction vessel may be placed in a separate heating device such as anoven to heat the monomer(s) and biodegradable polymeric material(s)contained therein.

The at least one monomer added to the reaction vessel may be any monomercapable of polymerizing via ring-opening polymerization. In embodiments,the at least one monomer may be a cyclic ester. Some examples ofsuitable cyclic esters include, but are not meant to be limited to,lactide, glycolide, p-dioxanone, ε-caprolactone, methyl-tetrahydrofuran,ω-pentadecalactone, ω-dodecalactone, δ-valerolactone,β-methyl-β-propiolactone, α-methyl-β-propiolactone, γ-butyrolactone,trimethylene carbonate, tetramethylene carbonate, 2,2-dimethyltrimethylene carbonate and combinations thereof.

The biodegradable polymeric materials described herein include at leastsome amount of residual catalyst from when the biodegradable polymericmaterial was previously formed. The residual catalyst may be composed ofat least one metal or metal compound selected from a group consisting ofIA group, IIA group, IIB group, IVA group, IVB group, VA group and VIIAgroup in the periodic table.

Residual catalysts classified in the IA group, for example, include ahydroxide of alkali metal (such as, for example, sodium hydroxide,potassium hydroxide, and lithium hydroxide), a salt of alkali metal withweak acid (such as, for example, sodium lactate, sodium acetate, sodiumcarbonate, sodium octylate, sodium stearate, potassium lactate,potassium acetate, potassium carbonate, and potassium octylate), and analkoxide of alkali metal (such as, for example, sodium methoxide,potassium methoxide, sodium ethoxide, and potassium ethoxide) andcombinations thereof.

Other residual catalysts include those classified in the: IIA group, forexample, a calcium salt of organic acids (such as, calcium acetate); IIBgroup, for example, a zinc salt of organic acid (such as, zinc acetate);IVA group, for example, tin powder may be mentioned as well as anorganic tin type catalyst (such as, for example, monobutylin, tinlactate, tin octonoate, tin 2-ethylhexanoate, tin tartrate, tindicaprylate, tin dilaurylate, tin diparmitate, tin distearate, tindioleate, tin α-naphthoate, tin β-naphthoate, and tin octylate); IVBgroup, for example, a titanium type compound such as tetrapropyltitanate and a zirconium type compound such as zirconium isopropoxide;VA group, for example, an antimony type compound such as antimonytrioxide; and, VIIA group, for example, a manganese salt of organic acid(such as, for example, manganese acetate).

All of these described above are conventionally known catalysts forring-opening polymerization of suitable monomers, such as lactic acid.Among these, the catalyst composed of tin or stannous octoate may be ofparticularly useful in view of catalytic activity. Various combinationsof catalysts, monomers, and polymeric materials may be utilized to forthe coated biodegradable polymeric materials described herein.

The residual catalyst may represent from about 0.01% to about 5% byweight of the biodegradable polymeric material prior to being processed.In certain embodiments, the residual catalyst may represent from about0.015% to about 3% by weight of the biodegradable polymeric materialprior to being processed.

It is envisioned that after processing of the biodegradable polymericmaterial in the reaction vessel, the amount of residual catalyst isreduced. In some embodiments, the amount of the residual catalyst may bereduced by at least 10%. In other embodiments, the amount of residualcatalyst may be reduced by at least 25%.

In some embodiments, the coated polymeric material may be catalyst freeor contain no residual catalyst. In certain embodiments, the coatedpolymeric material may contain minimal traces of residual catalyst; inembodiments less than about 0.005% by weight; in some embodiments lessthan about 0.001% by weight.

The biodegradable polymeric material may include any polymeric materialcapable of being formed via ring-opening polymerization. Somenon-limiting examples of suitable materials include at least one ofpoly-L-lactide, poly-DL-lactide, poly(lactic-co-glycolic acid),poly(glycolic acid), poly(p-dioxanone), poly(ε-caprolactone),poly(trimethylene carbonate), poly(tetramethylene carbonate),poly(hydroxylalkanoates), and combinations thereof.

Surface induced polymerization, as described herein, may be performed onbiodegradable polymeric materials in any form. For example, thebiodegradable material may be in the form of a biodegradable pellet,prior to further processing to form a finished product, such as abiodegradable implant or medical device. In other examples, thebiodegradable material may be in the form of a finished product. Someexamples of suitable products include sutures, staples, meshes, clips,screws, pins, rods, tacks, cables, occlusion devices, stents, andcombinations thereof. In particularly useful embodiments, thebiodegradable polymeric material is a fibrous material, such asmonofilament, multifilament, suture, staple fiber, mesh, and the like.

The biodegradable polymeric materials and the at least one monomer maybe positioned within the container for any suitable time necessary forthe polymeric materials and the monomer to interact and form a coatingon the polymeric material. In embodiments, the monomer(s) may have lowmelting points, i.e., below about 50° C., and the biodegradablepolymeric materials may have a glass transition point slightly above themonomers melting point, i.e., above about 50° C. This combination makesring-opening polymerization possible at lower temperatures and overlonger periods of time.

In some embodiments, the biodegradable polymeric materials and themonomers may be heated in the container for periods of time ranging fromabout 30 seconds to about 10 days. In other embodiments, thebiodegradable polymeric materials and the monomers may be heated in thecontainer for periods of time ranging from about 1 hour to about 7 days.In still other embodiments, the biodegradable polymeric materials andthe monomers may be heated in the container for periods of time rangingfrom about 4 hours to about 72 hours.

When heated, the monomer and/or polymeric material may be exposed totemperatures ranging from about 50° C. to about 100° C. In embodiments,the monomer and/or polymeric material may be exposed to temperaturesranging from about 60° C. to about 90° C. In certain embodiments, thetemperature inside the vessel will be made higher than the temperatureneeded for the catalyst and the monomer to polymerize but below thetemperature needed to further polymerize the polymeric material.

In some embodiments, the biodegradable polymeric materials and themonomers may be exposed to changes in pressure inside the container. Forexample, the pressure inside the container at anytime may be increasedto enhance the interaction between the monomers and the polymericmaterials. In another example, the container may include the polymericmaterial and prior to the introduction of the monomer into the containerthe pressure inside the container may be reduced to allow the polymericmaterial to expand slightly prior to the introduction of the monomerinto the container thereby enhancing the perfusion of the monomer intothe polymeric material. The pressure inside the container may range fromabout 0.1 to about 1 atm.

Methods wherein the coating of the biodegradable polymeric materials isperformed at reduced temperatures, i.e., below the crystallizationtemperature may allow for blends of various materials on a particulatelevel which may prevent phase separation problems commonly associatedwith other coating, blending, and/or extruding processes.

The coated biodegradable polymeric materials, such as an implantablemedical device, include a substrate formed from a biodegradablepolymeric material which includes a reduced amount of residual catalyst.The coating is attached to at least a portion of the substrate viainterpenetrating mechanisms through a surface of the substrate.

Turning to FIG. 1A, biodegradable polymeric material 120 a, i.e., apellet, is shown prior to processing and including residual catalyst130. Upon exposure to temperatures above the glass transitiontemperature of biodegradable polymeric material 120 a, the polymericmaterial will soften and the polymer chains will have increased mobilitythereby allowing the monomer and residual catalyst 130 to interact andform coating 122. As previously mentioned, the monomer may penetrate thesurface of the polymeric materials or the increased mobility of thepolymer chains may allow the residual catalyst to migrate to the surfaceto interact with the monomer. In FIG. 1B, biodegradable polymericmaterial 120 b is shown after processing and includes coating 122derived from monomers capable of ring-opening polymerization driven byresidual catalyst 130. Coating 122 is attached or grafted tobiodegradable polymeric material 120 b along a surface of biodegradablepolymeric material 120 b. Biodegradable polymeric material 120 bincludes a reduced amount of residual catalyst 130.

In embodiments, the coated pellets of biodegradable polymeric materialas described herein and shown in FIGS. 1A-1B may be further processedvia an extrusion or molding process to form a finished product, such asan implantable medical device. Since the polymeric material and thecoating are attached via the interpenetrating mechanisms, the blendingof the two materials during an extrusion and/or molding process is lesslikely to phase separate. Thus the phase separation problems frequentlyassociated with conventional polymer blends are avoided.

As shown in FIG. 2A, biodegradable polymeric material 220 a is animplantable medical device such as a suture. Biodegradable polymericmaterial 220 a includes residual catalyst 230. Upon exposure totemperatures above the glass transition temperature of biodegradablepolymeric material 220 a, the polymeric material will soften and regionswith a lower density may be created to allow the monomer and residualcatalyst 230 to interact and form coating 222. In FIG. 2B, biodegradablepolymeric material 220 b is shown after processing and includes coating222 derived from monomers capable of ring-opening polymerization drivenby residual catalyst 230. Coating 222 is attached or grafted tobiodegradable polymeric material 220 b via interpenetrating mechanisms226 along a surface of biodegradable polymeric material 220 b.Biodegradable polymeric material 220 b includes a reduced amount ofresidual catalyst 230.

Various combinations of monomers suitable for ring-openingpolymerization and biodegradable polymeric materials may be utilized inthe methods and devices described herein. The combinations may dependupon each materials different glass transition temperatures (Tg), andcrystallization temperatures (Tc). It is envisioned that thebiodegradable polymeric materials may be exposed to a temperatureslightly above the glass transition temperature and below thecrystallization temperature. It is further envisioned that thetemperature to which the biodegradable polymeric material is exposed issufficient for the polymerization of the monomer upon interaction withthe residual catalyst.

Example 1

Pellets containing high-molecular weight biodegradable resins, such asPurasorb PL 38 and Purasorb PLD, each including about 0.005% by weightstannous octoate, are positioned within a container with a monomer suchas p-dioxanone. The temperature is elevated to a between about 70-80° C.thereby softening the surface of the pellets and making the stannousoctoate more accessible to the p-dioxanone monomer. At that temperaturethe p-dioxanone will begin to polymerize following interaction with thestannous octoate along the surface of the pellets creating a surfacecoating grafted to the pellet. The pellets remain heated for about 24hours. Upon removal from the heat and/or container, the coated pelletsinclude about 0.001% by weight stannous octoate which is less than priorto processing.

Example 2

Filaments made from Purasorb PL 38 and Purasorb PLD and containing about0.005% by weight stannous octoate, are positioned within a containerwith a monomer such as p-dioxanone. The temperature is elevated to abetween about 70-80° C. thereby softening the surface of the filamentsand making the stannous octoate more accessible to the p-dioxanonemonomer. At that temperature the p-dioxanone will begin to polymerizefollowing interaction with the stannous octoate along the surface of thefilaments creating a surface coating grafted to the filaments. Thefilaments remain heated for about 8 hours. Upon removal from the heatand/or container, the coated filaments include about 0.003% by weightstannous octoate which is less than prior to processing. In addition, apoly-dioxanone coating is attached to the surface of the filaments

It will be understood that various modifications may be made to theembodiments disclosed herein. Thus, those skilled in the art willenvision other modifications within the scope and spirit of the claims.

What is claimed is:
 1. An implantable medical device comprising: asubstrate comprising a biodegradable polymeric material capable of beingformed via ring-opening polymerization and containing a reduced amountof residual catalyst; and a biodegradable coating positioned on at leasta portion of the substrate, wherein the biodegradable coating is derivedfrom at least one monomer capable of ring-opening polymerization by theresidual catalyst contained in the biodegradable polymeric material. 2.The implantable medical device of claim 1 wherein the implantablemedical device is selected from the group consisting of sutures,staples, meshes, clips, screws, pins, rods, tacks, cables, occlusiondevices, stents, and combinations thereof.
 3. The implantable medicaldevice of claim 1 wherein the implantable medical device is a suture. 4.The implantable medical device of claim 1 wherein the residual catalystcomprises at least one metal or metal compound selected from a groupconsisting of IA group, IIA group, IIB group, IVA group, IVB group, VAgroup and VIIA group in the periodic table.
 5. The implantable medicaldevice of claim 1 wherein the residual catalyst comprises stannousoctoate.
 6. The implantable medical device of claim 1 wherein thereduced amount of residual catalyst is less than about 0.005% by weightof the biodegradable polymeric material.
 7. The implantable medicaldevice of claim 1 wherein the reduced amount of residual catalyst isless than about 0.001% by weight of the biodegradable polymericmaterial.
 8. The implantable medical device of claim 1 wherein the atleast one monomer comprises a cyclic ester.
 9. The implantable medicaldevice of claim 8 wherein the cyclic ester comprises an aliphatic cyclicester.
 10. The implantable medical device of claim 8 wherein the cyclicester is selected from the group consisting of lactide, glycolide,p-dioxanone, ε-caprolactone, methyl-tetrahydrofuran, ω-pentadecalactone,ω-dodecalactone, δ-valerolactone, β-methyl-β-propiolactone,a-methyl-β-propiolactone, γ-butyrolactone, trimethylene carbonate,tetramethylene carbonate, 2,2-dimethyl trimethylene carbonate andcombinations thereof.
 11. The implantable medical device of claim 1wherein the monomer is ε-caprolactone and the substrate includespolylactide.
 12. The implantable medical device of claim 1 wherein themonomer has a melting temperature below about 50° C. and the substrateincludes a material having a glass transition temperature greater thanabout 50° C.
 13. The implantable medical device of claim 1 wherein thesubstrate includes a biodegradable polymeric material selected from thegroup consisting of poly-L-lactide, poly-DL-lactide,poly(lactic-co-glycolic acid), poly(glycolic acid), poly(p-dioxanone),poly(ε-caprolactone), poly(trimethylene carbonate), poly(tetramethylenecarbonate), poly(hydroxylalkanoates), and combinations thereof.
 14. Theimplantable medical device of claim 1 wherein the biodegradable coatingis continuous along the surface of the substrate.
 15. The implantablemedical device of claim 1 wherein the biodegradable coating isdiscontinuous along the surface of the substrate.
 16. A method ofinducing ring-opening polymerization of a cyclic ester monomer on asurface of a medical device comprising: providing a closed containerwhich includes a cyclic ester monomer capable of ring-openingpolymerization and medical device comprising a biodegradable polymericmaterial capable of being formed via ring-opening polymerization andincluding a residual catalyst; and heating the closed container to atleast a glass transition temperature of the biodegradable polymericmaterial of the medical device and below the crystallization temperatureof the biodegradable polymeric material of the medical device to inducering-opening polymerization of the cyclic ester monomer with theresidual catalyst contained in the biodegradable polymeric material. 17.A method of grafting a biodegradable coating onto a surface of abiodegradable polymeric material comprising: providing a container whichincludes at least one monomer capable of polymerizing via cationicring-opening polymerization and a pellet of a biodegradable polymericmaterial capable of being formed via ring-opening polymerization andcontaining a residual catalyst; placing the container with the pellet ofbiodegradable polymeric material in an oven for a period of time,wherein the oven is heated above the glass transition temperature andbelow the crystallization temperature of the biodegradable polymericmaterial; polymerizing the monomer with the residual catalyst containedin the biodegradable polymeric material to form a coated pellet; and,processing the coated pellet to form an implantable medical device. 18.The implantable medical device of claim 1 wherein the implantablemedical device is a mesh.
 19. The implantable medical device of claim 1wherein the biodegradable coating is grafted via interpenetratingmechanisms through a surface of the substrate.